Examining the Molecular Ion on a Mass spectrum

Without any structural information, we can estimate an upper limit on the number of carbons using the m/z for the molecular ion.

For the molecular ion at m/z 386.4 Da (shown in the mass spectrum below), the upper limit on the number of carbons is calculated at 386.4 / 12 = 32.2. Rounding down, we arrive at a maximum of 32 carbons. Therefore, one would expect the carbon count to be within a range of 0 to 32.

To estimate the upper range the # of Carbons ≈

(m/z for the Molecular Ion) / 12